The two-solution arcylic adhesive composition of this invention is composed of a solution A which has as its necessary ingredients (1) a chlorosulfonated polyethylene, (2) a (meth)acrylate monomer, and (3) an organic peroxide, and a solution B which has as its necessary ingredients (4) a butadiene-acrylonitrile copolymer elastomer (NBR), (5) a (meth)acrylate monomer, and (6) an aminealdehyde condensate.
Two-solution acrylic adhesives, characterized by containing various elastomer ingredients dissolved in reactive acrylic monomers and cured with redox catalysts, have been widely used for some time. Examples of such two-solution acrylic adhesives are those shown in Japanese Public Patent Disclosure Bulletins Nos. 49-132119, 51-7040, and 55-129740. As can be seen in these examples, the general method of bonding two objects together is that a (meth)acrylate solution containing a chlorosulfonated polyethylene and a polymerization initiator (main adhesive) is applied to one of the objects and a curing accelerator such as an amine-aldehyde condensate is applied to the other one; the two surfaces to which these solutions have been applied are then put into contact with each other. In this type of adhesive, since the acrylic monomer is graft-polymerized onto the chlorosulfonated polyethylene in the curing process, advantages are obtained in that the shrinkage rate is comparatively small, and there is excellent heat resistance. On the other hand, however, since a large quantity of chlorine is present in the chlorosulfonated polyethylene structure, there is the problem that when the adhesive is used on metal surfaces, and the parts to which the adhesive was applied are left under a high temperature for a long period, the aforementioned chlorine is eliminated and corrodes the metal surfaces. Moreover, there is the problem that, since the viscosities of curing accelerators containing amine-aldehyde condensates, etc., are low, the curing accelerator penetrates into the surface to which the adhesive is applied when the objects to which the adhesive is to be applied have porous surfaces, such as wood or foams. After the surfaces are adhered together the adhesive strength is uneven; moreover, since the quantity of curing accelerator used is very small, it is difficult to control the correct quantity that must be applied.
Therefore, it has been proposed that the curing accelerator solution be thickened with an acrylic resin (Japanese Public Patent Disclosure Bulletin No. 61-51072), or an epichlorohydrin rubber (Japanese Public Patent Disclosure Bulletin No. 56-74165).
However, the aforementioned acrylic rubbers have poor solubilities in (meth)acrylate monomers, and if the quantity compounded is increased, a gel is formed and uniform mixing is prevented. Moreover, the strength of the adhered layers after the two solutions are mixed and cured is still insufficient.
Acrylic resins have good solubilities in (meth)acrylate monomers, but it is necessary to compound a large quantity of such resins in order to obtain the target viscosity, and the rubber elasticity of the adhered layers which is obtained when a large quantity of the resin is compounded is lost, which is not desirable. Moreover, the spinnability of these resins is strong, which presents a problem of workability.
Epichlorohydrin rubber, in addition to having the same problems as aforementioned acrylic rubber, has a large quantity of chlorine in its molecule, like the chlorosulfonated polyethylene, and when it is exposed to high temperatures for long periods, the free chlorine corrodes the adhesion interface.
This invention was made with this situation in view, and has the purpose of providing a two-solution acrylic adhesive composition with excellent resistance to thermal deterioration and excellent workability.